Laser machining system and method

ABSTRACT

A substrate ( 16 ) is machined to form, for example, a via. The substrate is in a chamber ( 15 ) within which the gaseous environment is controlled. The machining laser beam ( 13 ) is delivered with control of parameters such as pulsing parameters to achieve desired effects. The gaseous environment may be controlled to control integral development of an insulating lining for a via, thereby avoiding the need for downstream etching and oxide growth steps. Also, machining may be performed in multiple passes in order to minimize thermal damage and to achieve other desired effects such as a particular via geometry.

[0001] The invention relates to laser machining of substrates.

[0002] Laser drilling of micro-vias with pulsed lasers may be performedusing two methods. In the first method a stationary beam is used (pixelvias): Using this technique a number of laser pulses are delivered to asingle point on the substrate. The number of pulses required to reach acertain depth depends on their energy. This technique is suitable forvias smaller than approximately 100 microns diameter. The exact viadiameter depends on the laser beam diameter, optical and laserparameters and material properties.

[0003] In another method a beam is scanned along the outer profile ofthe via. This technique is suitable for vias larger than approximately100 microns diameter. The laser moves in a circular pattern, in one ormore concentric circles. Several repetitions might be required to reachthe required depth. The via diameter is a function of the radius of theouter circle and the beam diameter. Such a via is referred to as ascanned or trepanned via.

[0004] Typically, using a laser beam to machine vias results in severalproblems. These problems result in the requirement for several postlaser machining process steps. Specifically the issues are:

[0005] Debris

[0006] During the laser drilling process debris on the topside of thewafer is caused by the accumulation of debris and molten material at thevia outlet. This is represented in FIG. A. It typically appears in twodistinct forms. In one form debris appears as a “lip” of materialsurrounding the via. The height of the lip can be several tens of ∉m. Itis believed that one of the processes that may contribute to theformation of the lip is the re-solidification of molten and gaseousmaterial ejected from the via during laser cutting. Typically the debriscannot be removed by conventional washing techniques. An ideal viashould have no debris or lip structures.

[0007] The second form of debris appears as a “dust” that covers on thetop surface of the wafer. Typically this debris can be removed by asimple wash process, however it is more favourable to eliminate thepresence of debris completely.

[0008] Sidewall Thermal Damage Zone

[0009] A second problem that occurs for via drilling is that theaccumulated heat in the material increases as the pulse rate, pulseenergy and total number of pulses of laser light into the material areincreased. At some point the heat dissipated into the surroundingmaterial can cause severe thermal damage to the internal walls of thestructure. The impact of thermal damage is to reduce structuralintegrity due to microcracking and crystal deformation. One technique toreduce this is to chop the beam so as to reduce the total energydelivered to the via. This however reduces the total energy delivered tothe surface and is not an efficient technique.

[0010] Sidewall Composition

[0011] Ultimately the objective of the via drilling process is toachieve an insulated microvia that can be metallized. It is essentialthat the via is structurally sound and that all reliability criteria canbe met. Using conventional techniques it is not possible to control thesidewall material composition or conductivity. To better understand therequirements of the via drilling process the full cycle is described inthe next section.

[0012] Where an insulating layer is required on the internal walls of amicrovia before insertion of a metal interconnect, two additionalprocesses subsequent to machining of the via are required. The first isto clean and smooth the via walls followed by a second process to growan insulating layer. This three-step process is illustrated in FIG. B.In step 1, a laser is used to machine a via structure with rough taperedwalls. A taper within a via is defined as the “slope” of the side wall,which is arctan(a/b) as shown in FIG. A. Step 2 is an cleaning stepwhereby the sidewalls of the via structure are cleaned. This preferablyresults in a smooth, high quality finish. In step 3, an insulating layeris created on the internal via walls.

[0013] The objectives of this invention are:

[0014] To provide a technique for laser drilling of micro-vias where theamount of debris on the topside of the via (the side from which the viais machined) is reduced.

[0015] To provide a technique for laser drilling micro-vias where theextent of the internal sidewall heat affected zone within the via isreduced.

[0016] To simplify the process of producing a via with desired side-wallmorphology, composition and optical and electrical properties.

[0017] To achieve greater versatility in use of laser-drilled vias.

[0018] To streamline the process of producing high quality viastructures with desired internal wall properties into a single stepprocess

[0019] To reduce the equipment set required in conventional viamanufacturing techniques

SUMMARY OF THE INVENTION

[0020] According to the invention there is provided a laser machiningsystem comprising a laser source, and a beam delivery system comprisingmeans for controlling delivery of a laser beam generated by the lasersource to a substrate to machine the substrate, wherein

[0021] the system further comprises a gas handling system comprisingmeans for providing a controlled gaseous environment around a machiningsite.

[0022] In one embodiment, the beam delivery system and the gas handlingsystem comprise means for controlling beam pulsing parameters and thegaseous environment to drill a via in the substrate.

[0023] In one embodiment, the beam delivery system comprises means forcontrolling laser pulse energy, laser pulse separation, and number ofpulses according to the optical, thermal, and mechanical properties ofthe material(s) being machined.

[0024] In one embodiment, the gas handling system comprises means forcontrolling proportion of oxygen in the gaseous environment to controlor prevent or promote oxide growth as a lining.

[0025] In one embodiment, the gas handling system comprises means forcontrolling proportion of nitrogen in the gaseous environment to controlor prevent nitride growth in a lining.

[0026] In one embodiment, the gas handling system comprises means forproviding a controlled amount of inert gas in the gaseous environment.

[0027] In one embodiment, the gas handling system comprises means forintroducing into the gaseous environment a gas which has properties fordissociation in the presence of the laser beam to provide etchants orreactants of the substrate.

[0028] In one embodiment, the gas handling system comprises means forcontrolling the gaseous environment to achieve a clean machined wall inthe substrate.

[0029] In another embodiment, the gas handling system comprises meansfor controlling the gaseous environment to achieve a desired smoothnessin a machined wall of the substrate.

[0030] In one embodiment, the gas handling system comprises means forcontrolling the gaseous environment to enhance removal of debris fromthe machining site and locality or to reduce the quantity of debris thatis generated.

[0031] In one embodiment, the beam delivery system comprises means forcontrolling pulsing parameters to minimise thermal damage to thesubstrate.

[0032] In one embodiment, the laser pulses are not evenly spaced intime.

[0033] In one embodiment, the beam delivery system comprises anon-telecentric lens, and means for delivering the laser beam throughsaid lens at an angle to normal to drill a sloped via.

[0034] In one embodiment, the beam delivery system comprises means forvarying distance of a sloped via entry opening from a beam optical axisto set slope of the sloped via.

[0035] In a further embodiment, the beam delivery system comprises meansfor drilling a via in the substrate and for dynamically varying laserbeam parameters as a function of current via depth.

[0036] In one embodiment, the beam delivery system comprises means forvarying laser beam parameters according to material of the substrate atany particular depth.

[0037] In one embodiment, the beam delivery system comprises means forvarying laser beam parameters with depth in order to achieve a desiredvia geometry.

[0038] In one embodiment, said varying means comprises means for varyingthe laser beam parameters to drill a blind via.

[0039] In one embodiment, the beam delivery system comprises means forvarying laser beam parameters with depth in order to achieve acontrolled via diameter at the entrance and exit points on thesubstrate.

[0040] In one embodiment, the varying means comprises means forcontrolling slope of a taper between the entry and exit openings byvarying laser repetition rate, pulse energy, and pulse peak power.

[0041] In one embodiment, the varying means comprises means for varyingfocal spot size to control internal via shape.

[0042] In one embodiment, the beam delivery system comprises atelescope, and means for adjusting the telescope to set or dynamicallyvary beam diameter, plane of focus, and depth of focus to provide adesired via geometry.

[0043] In one embodiment, the beam delivery system comprises means formachining the substrate in a plurality of passes, in which each passmachines to a certain stage with a proportion of material removal.

[0044] In one embodiment, the beam delivery system comprises means foradjusting the telescope between passes.

[0045] In one embodiment, the beam delivery system comprises means forenlarging laser beam focal spot size after drilling a via to cause lasercleaning of debris on the surface of the substrate surrounding the via.

[0046] In one embodiment, the gas handling system and the beam deliverysystem comprise means for controlling laser pulsing and the gaseousenvironment to provide a controlled insulating lining in a via drilledin a semiconductor substrate.

[0047] In one embodiment, the substrate is of Si material and the liningis SiO₂.

[0048] In one embodiment, the gas handling system comprises a sealedchamber, means for delivery of gases into the chamber and means forpumping gases from the chamber.

[0049] In one embodiment, the chamber comprises a window which istransparent to the laser beam.

[0050] In one embodiment, the gas handling system comprises means fordelivering a halogenated gas to the gaseous environment to removegaseous debris.

[0051] In one embodiment, herein the gas handling system comprises meansfor controlling gas flow for removal of debris in both gaseous andparticulate form.

[0052] In one embodiment, the system further comprises means forflipping a substrate, and the beam delivery system comprises means fordrilling at locations in registry at opposed substrate surfaces tocomplete a through via.

[0053] In one embodiment, the beam delivery system and the gas handlingsystem comprise means for controlling beam pulsing parameters and thegaseous environment to drill a via having a lining suitable for use asan electrical insulator.

[0054] In one embodiment, the beam delivery system and the gas handlingsystem comprise means for controlling beam pulsing parameters and thegaseous environment to drill a via having a lining suitable for use asan optical waveguide cladding.

[0055] The invention also provides a laser machining method comprisingthe steps of delivering a laser beam onto a substrate to machine thesubstrate, wherein

[0056] a gaseous environment is provided around a machining site;

[0057] the laser beam is pulsed; and

[0058] the laser beam and the gaseous environment are controlled tomachine the substrate to achieve desired properties in the substrate.

[0059] In one embodiment, laser pulse energy, laser pulse separation,and number of pulses are controlled according to substrate optical,thermal, and mechanical properties.

[0060] In one embodiment, oxygen or nitrogen concentration in thegaseous environment is controlled to control or prevent oxide or nitridegrowth as a via lining.

[0061] In one embodiment, a controlled amount of inert gas is introducedinto the gaseous environment.

[0062] In one embodiment, a gas having properties for dissociation inthe presence of the laser beam is introduced into the gaseousenvironment, and the dissociated gases etch the substrate.

[0063] In one embodiment, the machining is to drill a via and laser beamparameters are dynamically varied as a function of current via depth.

[0064] In one embodiment, the laser beam and the gaseous environment arecontrolled to provide an electrically insulating lining, and the methodcomprises the further step of filling the via with an electricallyconducting material to provide an electrical conductor in the substrate.

[0065] In one embodiment, the laser beam and the gaseous environment arecontrolled to provide an optically opaque lining, and the methodcomprises the further step of filling the via with an opticallytransmissive material to provide an optical waveguide in the substratewith the lining as a cladding.

[0066] In one embodiment, the laser beam and the gaseous environment arecontrolled to provide a thermally conductive path, and the methodcomprises the further step of filling the via with a thermallyconductive material to provide a thermally conductive path in thesubstrate.

[0067] In one embodiment, the method comprises the further step ofconnecting a heat sink to the thermally conductive material in the via.

[0068] The invention also provides a laser machining system comprising alaser source, and a beam delivery system comprising means forcontrolling delivery of a laser beam generated by the laser source to asubstrate to machine the substrate, wherein

[0069] the beam delivery system comprises means for delivering a pulsedlaser beam to a substrate; and

[0070] the beam delivery system comprises means for machining thesubstrate to an incomplete stage at a plurality of machining sites, andfor machining at said sites in at least one subsequent pass wherebythere is a delay between machining at any one site as the other sitesare machined in a pass.

[0071] In one embodiment, the beam delivery system comprises means forchanging beam delivery parameters between passes.

[0072] In one embodiment, the beam delivery system comprises means forchanging beam delivery parameters between passes according to thesubstrate layer material for a pass.

[0073] In one embodiment, the beam delivery system comprises means forchanging beam delivery parameters between passes according to desiredsubstrate shape at the machining sites.

[0074] In one embodiment, the beam delivery system comprises means forcontrolling beam delivery parameters between passes to minimisesubstrate thermal damage.

[0075] In one embodiment, the beam delivery system comprises means forcontrolling beam delivery parameters between passes to reduce depositionof debris.

[0076] In one embodiment, the beam delivery system comprises means forcontrolling beam delivery parameters between passes to achieve a desiredsubstrate geometry at the machining sites.

[0077] In one embodiment, the beam delivery system comprises means forcontrolling beam delivery parameters between passes to drill a pluralityof vias in the substrate.

[0078] In one embodiment, herein the system further comprises means forflipping a substrate and the beam delivery system comprises means formachining the substrate at machining sites on opposed sides of thesubstrate in registry to machine a single formation.

[0079] In one embodiment, the beam delivery system comprises means forcontrolling beam delivery parameters to both machine the substrate andto form an electrically insulating lining at the machined site.

[0080] In one embodiment, the system also has a gas handling system inwhich the gas and gas parameters may be changed between subsequentpasses.

[0081] In one embodiment, the system further comprises a gas handlingsystem comprising means for providing a controlled gaseous environmentaround the machining site, and the beam delivery system and the gashandling system comprise means for machining a formation in thesubstrate with or without non-ambient gas in one pass, and for machiningat the site in a subsequent pass with a non-ambient gaseous environmentto form an insulating lining at the machining site.

[0082] The invention also provides a laser machining method comprisingthe steps of delivering a laser beam onto a substrate to machine thesubstrate, wherein the beam is delivered to machine the substrate at aplurality of sites in a pass, and to subsequently drill at the samesites in at least one subsequent pass to complete machining at eachsite.

[0083] In one embodiment, a via is drilled at each site.

[0084] In one embodiment, beam delivery is controlled to both machine aformation at each site and to provide an electrically insulating liningon a substrate wall at each site.

[0085] In one embodiment, a controlled gaseous environment is providedat the machining sites to assist lining growth in a controlled manner.

[0086] In one embodiment, the system is used in a manner in which thegas and gas parameters may be changed between subsequent passes.

[0087] The invention also provides a laser machining system comprising alaser source, and a beam delivery system comprising means forcontrolling delivery of a laser beam generated by the laser source to asubstrate to machine the substrate, wherein the beam delivery systemcomprises means for delivering a pulsed laser beam to a substrate at anangle to drill a sloped via.

[0088] The invention also provides a laser machining method comprisingthe steps of delivering a laser beam onto a substrate to machine thesubstrate, wherein the laser beam is pulsed, and the beam is deliveredat an angle to drill a sloped via.

[0089] In one embodiment, the via is drilled to interconnect layers inthe substrate.

[0090] In one embodiment, the via is drilled for conformity withcomponent leads to be mounted on the substrate.

[0091] In one embodiment, a plurality of interconnecting vias aredrilled.

[0092] In one embodiment, the vias are drilled to interconnect at thesubstrate surface.

[0093] In one embodiment, herein the vias are drilled to interconnectinternally within the substrate and to each have a separate opening in asubstrate surface.

[0094] The invention also provides a laser machining method comprisingthe steps of delivering a laser beam onto a substrate to machine thesubstrate, wherein the laser beam is pulsed and is delivered to drill avia in the substrate, and the method comprises the further step offilling the via with a thermally conductive material to provide athermal conductor.

[0095] In one embodiment, the method comprises the further steps ofconnecting a heat sink to the thermally conductive material.

[0096] In one embodiment, the method comprises the further step ofdrilling another via adjacent to said via and filling said other viawith an electrically conductive material, and connecting an electricalcomponent to said electrically conductive material.

[0097] In one embodiment, the via is a blind via.

[0098] In one embodiment, the angled vias are generated in a geometrythat allows multiple via contact points on one side of a substrate to asingle contact point on the other side of the substrate.

[0099] In one embodiment, multiple power inputs and outputs or multipleground inputs and outputs are consolidated to a reduced number inputsand outputs.

[0100] In one embodiment, angled vias are used to reduce the size of adevice by allowing connection pads to be placed on the back side of thedie.

[0101] In one embodiment, the laser source is a solid state diode pumpedlaser.

[0102] In one embodiment, the laser is a frequency multiplied solidstate laser.

[0103] In one embodiment, the laser is a solid state laser where thelaser medium is of the type Host:Impurity where the host is YAG, YLF,Vanadate.

[0104] In one embodiment, the laser repetition frequency is in the rangefrom 1 kHz to 200 kHz.

[0105] In one embodiment, the laser pulsewidth is less than 200nanoseconds.

[0106] In one embodiment, the laser pulsewidth is less than 10nanoseconds.

DETAILED DESCRIPTION OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS

[0107] The invention will be more clearly understood from the followingdescription of some embodiments thereof, given by way of example onlywith reference to the accompanying drawings in which:

[0108]FIG. 1 is a diagram illustrating laser drilling of a through viaaccording to the invention;

[0109]FIG. 2 is a diagram illustrating a laser machining system used forvia drilling in a controlled gaseous environment;

[0110]FIG. 3 is a diagram illustrating steps for drilling of multiplevias using a multi-step laser process;

[0111]FIG. 4 is a plot of a laser pulse train illustrating the variables

t_(RR), N_(T) _(—) _(Delay) and T_Delay;

[0112]FIG. 5(a) is a view of the wafer subdivided into rectangles ofequal in area to the galvanometer field of view, and

[0113]FIG. 5(b) is an expanded view of FIG. 5(a) showing a typicalgalvanometer field of view where d₁, d₂ and d₃ are the distances betweenvia structures;

[0114]FIG. 6 is a plot of ablation depth vs. number of laser pulses;

[0115]FIG. 7 is a diagram showing drilling through successive layers ofa multi-layered substrate using a multi-step laser process;

[0116]FIG. 8 is a diagram illustrating drilling of a substrate on bothsides to complete a through via;

[0117]FIG. 9 is a diagram showing a multi-step laser machining processfrom both sides of the substrate in order to achieve a profiled viainternal sidewall;

[0118]FIGS. 10, 11 and 12 are diagrams illustrating optical parametersfor laser drilling;

[0119]FIG. 13 is a diagram showing the area surrounding a via over whicha defocused laser beam is placed for laser cleaning;

[0120]FIG. 14 a set of views of a substrate of an opto-electroniccomponent of the invention;

[0121]FIG. 15 is a perspective view showing the top surface of thesubstrate in more detail;

[0122]FIGS. 16 and 17 are diagrams showing formation of a V-shapedgroove for an optical fibre;

[0123]FIG. 18 is a perspective view of an optical fibre;

[0124]FIG. 19 is a perspective view illustrating vias in more detail;and

[0125]FIGS. 20, 21, and 22 are diagrams illustrating drilling of angledvias;

[0126]FIG. 23(A) is a diagram showing conventional location of pads andsolder balls on the same side of the die as the active device

[0127]FIG. 23(B) is a diagram showing the relocation of pads and solderballs on the back side of a wafer that is accessed using laser machinedvia structures; and

[0128]FIG. 24 illustrates the connection of four I/O points of an activedevice to a common ground or common power point on the bottom of a wafer

DESCRIPTION OF THE EMBODIMENTS

[0129] A substrate is machined to provide a formation such as a via inthe substrate. There is excellent control over the sidewall physicalmorphology, structural integrity and composition. Also, there isexcellent control over the amount and location of debris generated.Also, the invention provides improved versatility for via laserdrilling, whereby blind. vias, multilayer vias, and angled vias may bedrilled in a simple and effective manner.

[0130] Before describing the drilling mechanism, the beam pulsingparameters are presented as below:

[0131] Machining Speed (V_(mach))

[0132] This parameter is defined as the number of vias that can bedrilled in each second. The unit of machining speed is the number ofvias per second. It is always the intention to optimise this parameterto the highest value, while maintaining acceptable cut quality.

[0133] Via Cutting Time (T_Delay)

[0134] This parameter is defined as the time the galvo will remain at aparticular via position during a given laser machining step. The depthof the via drilled will be proportional to T_Delay. Normally thisparameter is optimised to the lowest possible value in order to obtainthe highest machining speed (V_(mach)) with acceptable via quality. Theoptimum T_Delay for a via machining process will vary according to thephysical properties (such as thermal conductivity) of the material to bemachined, plasma expansion/relaxation time, distance between vias, viaquality, laser pulse energy and other parameters. A higher T_Delay willtypically cause more thermal damage to the via structure.

[0135] Single Pulse Period (

t_(RR))

[0136] This parameter is defined as the temporal distance between laserpulses in a pulse train and is essentially the inverse of laserrepetition rate:$\ni {t_{R\quad R}\quad \frac{1}{{Repitition}\quad {Rate}}}$

[0137] For example, for a laser repetition rate of 45 kHz,

t_(RR)˜22 ∉s.

[0138] Number of Pulses (N_(T) _(—) _(Delay))

[0139] This parameter is defined as the number of pulses to be deliveredto a certain via position during a given laser machining step. T_Delay,

t_(RR) and N_(T) _(—) _(Delay) are related to each other by thefollowing expression:

T _(—) Delay=N _(T) _(—) _(Delay)υ

t _(RR)

[0140] These parameters are depicted in FIG. 4.

[0141] Number of Steps (N_(Step))

[0142] This parameter is defined as the total number of steps requiredto machine a single via structure to the required depth. The totalnumber of steps will determine the depth of the via that is drilled.

[0143] Density of Vias (N_(Via/field)) p This parameter is defined asthe total number of vias within the permitted working field of view ofthe galvonometer(galvanometer) scanner. N_(Via/field) is illustrated inFIG. 5.

[0144] Distance between Vias (d_(Via))

[0145] This parameter is defined as the distance between two vias, andnormally is different from via to via. d_(Via) is illustrated in FIG. 3and FIG. 5.

[0146] Galvo Jump Speed (J_Speed)

[0147] This parameter is defined as the speed of the galvanometermovement between two via structures and is measured in units of metersper second (ms⁻¹). A higher value of J_Speed results in an increase inmachining speed.

[0148] Jump Delay (J_Delay)

[0149] This parameter is defined as the settling time for thegalvanometer after moving to a new via position. If J_Delay is too shortthis will result in a “spiking” laser line around the via due toinsufficient time for the galvanometer mirrors to settle followingmovement from one via to the next. However, a long J_Delay will resultin a lower machining time. A higher galvo jump speed (J_Speed) normallyrequires a higher jump delay (J_Delay), and hence the optimisation ofthese two parameters is essential in order to obtain the highestmachining speed with acceptable cut quality.

[0150] Optical Parameters

[0151] Beam Diameter

[0152] Beam diameter refers to the 1/e squared diameter of the spatialintensity profile of the laser. In via machining, the diameter of thevia is a function of the beam diameter. Beam diameter is a variable thatcan be controlled through selection of the focusing lens, scanlens orbeam telescope. The effect of modifying beam diameter is to modify thepower density level at focus.

[0153] Peak Power Density (Intensity)

[0154] This parameter is defined as the peak power per unit area, wherethe peak power is the energy per second.${P\quad e\quad a\quad k\quad P\quad o\quad w\quad e\quad r\quad D\quad e\quad n\quad s\quad i\quad t\quad y} = \frac{E}{\ni {t\quad \upsilon \quad A}}$

[0155] Where E is the energy in Joules,

t is the pulse width in seconds and A is area in centimeters squared andthe peak power density is in Watts per centimeter squared.

[0156] Energy Density ${{Energy}\quad {Density}} = \frac{E}{A}$

[0157] This parameter defined as the energy (E) in Joules divided by thearea (A) in centimeters squared. The unit of energy density is Joulesper centimeter squared.

[0158] Depth of Focus

[0159] The depth of focus for focused beams of second, third and fourthharmonic YAG, YLF and Vanadate type lasers is larger than in multimodelasers and in lasers with large M squared values. This is primarily dueto the fact that the spatial output from YAG, YLF and Vanadate typelaser systems is Gaussian. A large depth of focus is highly advantageousfor via machining in thick wafer substrates, as generally the waferthickness is such that it can be placed at a fixed distance from theworking lens without repositioning to compensate for defocusing effects.However, under certain circumstances, the beam may require certaindefocusing in order to improve the wall quality or taper angle withinthe via.

[0160] Formation of Through Hole Micro-Vias

[0161] Referring to FIG. 1 a substrate 1 is drilled with an insulatinglayer on the via side-wall 2 by controlled laser pulses 3 and/or acontrolled gas flow 4. A substrate is defined as a workpiece to bemachined, which may include but is not limited to wafers and othersemiconductor, electronic or optoelectronic device. This substrate mayconsist of a single material, or a combination of materials including,but not limited to, a layered structure consisting of a single materialor multiple materials, and these materials may or may not be patterned.

[0162] Combining the control of laser pulses and gas flow or using justone of these individual processes will enable machining of vias withsignificantly reduced debris and significantly reduced sidewall thermaldamage. For example a smooth, high quality internal wall surface and alow degree of via taper can be produced using a multi-step lasermachining process whereby a controlled number of laser pulses (withvariable inter-pulse separation and pulse energy) are delivered to thesubstrate within a certain time period. This reduces thermal damage tothe via sidewalls, thus resulting in smooth internal side-walls.

[0163] A laser controller controls the laser pulse energy, inter-pulseseparation and the number of pulses per laser machining step on thebasis of the optical, thermal and mechanical properties of the materialto be machined, the machining depth within the substrate material andalso the laser type to be used.

[0164] A gas handling system controls the gaseous environment. In oneembodiment, the environment includes photo-activated etchants of thesubstrate material. The oxygen concentration in the environment isselected to remain constant or to vary during machining of the viastructure, thus promoting growth of an oxide layer on the internal viawalls during laser machining. Control of the oxygen concentration or theconcentration of oxygen containing gases (e.g. CO₂) permits control ofthe oxide layer thickness required for electrical insulation of atypical metal interconnect inserted into a via machined in a siliconsubstrate.

[0165] Referring to FIG. 2 a laser machining system 10 comprises agalvanometer 11 and a telecentric lens 12 providing a Q-switched UVlaser beam 13. The beam 13 is directed onto an access window 14 of acleanroom chamber 15 containing a wafer 16 to be drilled. The system 10comprises gas inlets 17 and a vacuum pumping lines 18 for the chamber15. The chamber 15 is mounted on an X-Y translation stage.

[0166] Laser light enters the window 14 of the gas reaction chamber 15,which is capable of withstanding pressures of up to 10 bar.Alternatively, this chamber can be evacuated to typical pressures in theregion of 0.1 bar for machining at pressures below atmosphere. Differentgases are introduced into the chamber 15 by the series of mass flowcontrollers 17, which permit control of the relative gas concentrationsin the chamber 15 for laser machining in a static gas environment. Also,the mass flow controllers 17 and 18 on the inlet and vacuum outlet linespermit control of the flow rate of different gases for machining in anon-static gas environment.

[0167] The vacuum exhaust line 18 permits evacuation of the chamber 15below atmospheric pressure and is also used to vent waste gaseousproducts produced during the laser machining process. A filter connectedto the vacuum line permits filtering of unwanted waste products andrecycling of unused gases. A detector connected to the chamber 15permits measurement of the relative and absolute concentrations ofparent gases and by-products produced during laser machining.

[0168] Smooth internal via walls are achieved by varying the laser pulseenergy and the inter-pulse separation at different steps throughout themulti-step process used to machine a single via structure. This permitscontrol of thermal loading in the substrate to be machined, thuspreventing excess damage of the via side walls due to thermal stress.

[0169] Also, introduction of fluorocarbon gases (e.g. CF₄) into thechamber 15 during machining of the via structure results in reduceddebris machining as photo-dissociated fluorine assists in siliconremoval in a gaseous form. Other photo-activated gases used in lowdebris machining of silicon in the gas reaction chamber include, but arenot limited to, chlorofluorocarbons and halocarbons.

[0170] By combining the above two process, a superior quality via can beachieved.

[0171] Laser machining of via structures in an inert gas environmentsuch as helium and argon permits suppression of oxide growth on theinternal via side-walls for applications requiring non-insulatingside-walls. The introduction of nitrogen into the gas reaction chamberduring machining permits growth of the insulating material siliconnitride on the internal via side-walls for applications requiringnon-insulating side walls.

[0172] Following laser machining, a layer is formed on the internalside-wall of the via structure. This layer is formed when substratematerial, melted during laser machining, re-solidifies upon cooling.Through suitable choice of gas mixes, their flow rates and theirrelative concentrations the stoichiometry, microstructure and otherproperties of this layer can be altered so as to produce a side-wallwith electrical and/or optical properties best suited to the desiredapplication. Gas mixes include: Active (e.g. O₂, CO₂)+Inert gases (e.g.He, Ar) for control of oxide growth in the via internal side-walls,Nitrogen+Inert gases (e.g. He, Ar) for control of nitride growth in thevia internal side-walls, Active (e.g. O₂, CO₂) or Nitrogen+Etchant gas(e.g. chlorofluorocarbons, halocarbons) for control of oxide or nitridegrowth in the via internal side-walls with reduced surface roughness andreduced debris inside and outside the via structure.

[0173] Multi-Step Micro Via Machining

[0174]FIG. 3 shows the basic operation of a multi step via machiningstrategy. In this strategy, the laser beam stays at a single viaposition for a certain predetermined period of time (i.e. T_Delay) andwill then be moved to another via position. The laser beam will thenmove back to the first via position after it has finished cutting thelast via. This procedure is repeated another (N_(Step-1)) times. Onepurpose of the ‘multi’ step approach is to reduce the heat affected zone(HAZ) within the via, which is believed to contribute to debris and todowngrade the side-wall quality of the via. Also, by changing the laserpulse and beam properties at different steps in a multi-step process,mulitlayer structures consisting of different materials can beefficiently machined during each step.

[0175] Machining Speed (V_(mach))

[0176] The machining speed as a function of other laser processingparameters can be derived as follows:

[0177] For a given galvanometer field of view as depicted in FIG. 5.$\begin{matrix}{\begin{matrix}{{Time}\quad {required}\quad {to}\quad {cut}\quad a} \\{{single}\quad {step}\quad {for}\quad a\quad {via}}\end{matrix} = {T\_ Delay}} \\{= {{N_{T\_ Delay}\quad \upsilon} \ni t_{R\quad R}}}\end{matrix}$ $\begin{matrix}{\begin{matrix}{{Total}\quad {time}\quad {required}\quad {to}} \\{{cut}\quad a\quad {single}\quad {step}\quad {for}} \\{{all}\quad {vias}{\quad \quad}{to}{\quad \quad}{be}{\quad \quad}{machined}\quad \left( t_{1} \right)}\end{matrix} = {N_{{via}/{field}}\quad \upsilon \quad {T\_ Delay}}} \\{t_{1} = {{N_{{via}/{field}}\quad \upsilon \quad N_{T\_ Delay}\quad \upsilon} \ni t_{R\quad R}}}\end{matrix}$

[0178] The total jump distance of the galvanometer for a single cuttingstep=the total distance (d_(Via)) travelled by the galvanometer forN_(Via/field) number of vias$= {\underset{i\quad l}{\overset{i\quad N_{{via}/{field}}}{f}}d_{V\quad i\quad a}}$

[0179] The total galvanometer jump time required to machine a singlestep for N_(Via/field) number of vias (t₂)$= \frac{{\underset{i\quad l}{\overset{i\quad N_{{via}/{field}}}{f}}d_{V\quad i\quad a}}\quad}{J\_ Speed}$

[0180] The total galvanometer setting time during machining of a singlestep for N_(Via/field) number of vias (t₃)

[0181] =J_DelayυN_(via/field)

[0182] The total time required to complete a single via drilling stepfor N_(Via/field) number of vias

[0183] =t₁+t₂+t₃

[0184] Assuming all the beam parameters are remain unchanged throughoutall the process steps, the total time required to complete all viadrilling steps in a multistep process for a single galvanometer field ofview is

[0185] =N_(step)υ(t₁+t₂+t₃) $\begin{matrix}\begin{matrix}{\begin{matrix}{{{The}\quad {number}\quad {of}{\quad \quad}{vias}\quad {drilled}\quad {per}}\quad} \\{{second}\quad \left( {{i.e}\quad {Machining}\quad {Speed}\quad {or}\quad V_{mach}} \right)}\end{matrix} = \frac{N_{{via}/{field}}}{N_{Step}{\upsilon \begin{pmatrix}t_{1} & t_{2} & t_{3}\end{pmatrix}}}} \\{= \frac{N_{{via}/{field}}}{N_{Step}{\upsilon \left\lbrack {{N_{{via}/{field}}\upsilon \quad N_{T\_ Delay}\upsilon} \ni {t_{R\quad R}\begin{matrix}\clubsuit \\◆ \\◆ \\◆ \\◆ \\\heartsuit\end{matrix}\frac{{\underset{i\quad l}{\overset{i\quad N_{{via}/{field}}}{f}}d_{V\quad i\quad a}}\quad}{J\_ Speed}\begin{matrix}\bullet \\ \div \\ \div \\ \div \\ \div \\ \neq \end{matrix}{J\_ Delay\upsilon N}_{{via}/{field}}}} \right\rbrack}}}\end{matrix} & (1.1)\end{matrix}$

[0186] From the expression (1.1) above, it is clearly indicates that oneof the critical parameters that determines the machining speed isN_(Step), i.e. the lower the N_(Step) the higher the machining speed.Since the total number of pulses that is required to machine a via isconstant at a certain thickness of the machined material, one of thepossible ways to reduce N_(Step) is to increase the number of pulsesfired (N_(T) _(—) _(Delay)) in each step. However, an increase in N_(T)_(—) _(Delay) may introduce thermal damage in the via structure due tothe fact that a higher number of pulses is directed on each via at eachinstant. These two parameters are optimised in order to obtain thehighest machining speed with the best via quality.

[0187] Expression (1.1) also shows that the machining speed isproportional to J_Speed but inversely proportional to J_Delay. A higherJ_Speed (hence higher machining speed) requires a longer J_Delay (i.e.higher galvanometer setting time), which will in turn reduce the overallmachining speed. For a given substrate material and laser type, thesetwo parameters are optimised in order yield the highest machining speed.

[0188] As shown in expression (1.1), another parameters that determinesthe machining speed is the laser repetition rate, i.e. the higher therepetition rate, the lower the

t_(RR) and hence the higher the machining speed. This can be understoodas more pulses is delivered to the via in higher repetition rate whichwill increase the overall machining speed. However, a laser pulseoperated in higher repetition rate may result in a lower average powerdue to the natural characteristics of the laser. Furthermore, a higherrepetition rate also has the potential to cause more thermal damage onthe side wall as more pulses are delivered to the via in a shorterperiod. For a given type of laser, this parameter is optimised to yieldthe highest machining speed with the best via quality.

[0189] Expression (1.1) also shows that the machining speed is inverselyproportional to the total distance between via  $\left( {{i.e.\quad \underset{i\quad 1}{\overset{i\quad N_{{Via}/{field}}}{f}}}d_{via}} \right),$

[0190]  i.e. the longer the distance, the lower the machining speed. Aspart of this invention a software algorithm has been developed todetermine the most ‘effective’ (i.e. shortest) distance travelled bygalvanometer for a given set of via distributions within the galvo fieldin order to obtain the highest possible machining speed.

EXAMPLE 1

[0191] In a process of drilling 1000 vias in a galvo field of 15 mmυ15mm at a laser repetition rate of 55 kHz, using two pulses on each viaand 50 machining steps, for a jump speed of 5 m/sec and a jump delay of50 ∉s. The total distance between all the vias is 0.48 m.

[0192] The machining speed can be estimated as below:${\ni t_{R\quad R}} = {\frac{1}{55000} = {{18.19\Pi \quad s} = {18.19{\upsilon 10}^{- 6}\quad {\sec.}}}}$

[0193] N_(Via/field)=1000

[0194] J_Speed=5 m/sec

[0195] J_Delay=50 ∉s=50υ10⁻⁶ sec

[0196] N_(T) _(—) _(Delay)=2 (for 2 pulse on each step)

[0197] N_(Step)=50 $V_{mach} = {{\left. \frac{1000}{\begin{matrix}{\begin{matrix}{50\underset{\leftarrow}{\overset{\spadesuit}{\leftrightarrow}}{1000{\upsilon 2\upsilon 18}.19{\upsilon 10}^{6}}} & \begin{matrix}\clubsuit \\◆ \\\heartsuit\end{matrix}\end{matrix}\frac{0.48}{5}\begin{matrix}\bullet \\ \div \\ \neq \end{matrix}} & {50{\upsilon 10}^{6}{\upsilon 1000}}\end{matrix}\begin{matrix} = \\ \approx \\¨\end{matrix}} \right.\sim 110}\quad {{vias}/{\sec.}}}$

[0198] The above example describes a specific case where the laser pulseparameters remain unchanged throughout the multi-step process. However,if the laser pulse properties such as inter-pulse separation (

t_(RR)) and the number of pulses per step (N_(T) _(—) _(Delay)) changefrom step to step, the denominator of equation (1.1) need to be replacedby the total sum of t1, t2 and t3 for each step.

[0199] Formation of Blind Microvias

[0200] Through-hole micro-vias enable connectivity between top andbottom surfaces of a substrate However, in certain applications where itis not required that the via structure is completely drilled through thesubstrate material, a blind via is formed. An example of an applicationrequiring such a via type is where conductive layers lie within asemiconductor or dielectric stack and it is necessary to drill partiallythrough the wafer down to the conductor without defacing or damaging theconductor. In this specific example of the via drilling process themetal is unharmed and retains its integrity, the debris produced duringmachining does not block the conductive path, and the via is fullydrilled through to the metal or conductor.

[0201] An example of a structure like this is shown in FIG. 7. As anexample the top layer may be crystalline silicon of thickness Dx+dz,below it is a copper layer of thickness c and below it is another layerof silicon.

[0202] In one embodiment of the invention it is required to drill a viadown to the level of metal, without damaging the metal. In thatinstance, the via is drilled to depth Dx using normal via machiningparameters. To drill to the metal layer the laser power, repetitionfrequency and pulse energy may be modified to remove the thickness dz ata slower rate. This ensures that excess energy is not dissipated in theconductive metal layer and that a clean contact is left to the top ofthe metal thin film. Additionally, performing this machining process inthe presence of a photo-activated etchant gas or/and multistep processwill aid this process.

[0203] In another embodiment it is required to drill though the copperat this point, without damaging the underlying silicon layer. In thatcase the above two steps are repeated, and then the laser drillingparameters are altered again so to drill through the copper withoutdamaging the underlying silicon.

[0204] In a further embodiment the semiconductor structure may be astacked structure of semiconductor, dielectric (e.g. polymer, quartz,glass) and/or metal materials. Depending on the layer the via drillingparameters (pulse separation, pulse energy, average power, laser foalspot size etc.) may be modified to ensure optimised machining througheach layer of the multilayer structure. Modifying the parameters in thisway ensures that defects such as de-lamination, melting and debris areminimised.

[0205] Control of Via Depth and Shape

[0206] When drilling vias through a semiconductor, the ablation depthincreases logarithmically with the number of laser pulses. This isrepresented approximately for silicon in FIG. 6. In summary, machiningvias in thin wafers is exponentially faster than in thicker wafers. Thisdata is true if the via drilling parameters are held constant.

[0207] A second impact of the above observation is that the taper of themicrovia is dependent on the laser parameters used to machine the via.Specifically, peak power and average power.

[0208] To improve the removal of material at points deeper in thesubstrate it is beneficial to modify the laser parameters so that pulseswith higher peak power are used. This approach enables more efficientremoval of material in deeper vias and also enables control of the microvia taper.

[0209] In a further embodiment, the via may be formed by first machiningfrom one side of the wafer to a depth d1 and by flipping the wafer anddrilling to a dept d2 in registration with the via on the other side ofthe wafer, the complete via of depth d1+d2 may be drilled. This isrepresented in FIG. 8. The effect of this is to eliminate taper andensure that top and bottom diameter are identical and also, as the depthof machining is faster for thinner wafers (or for reduced depth vias)the total number of pulses required is significantly less than in thecase of drilling from one side.

[0210] Another embodiment of the invention relates to scanning the beamin a circle or series of concentric circles with a specific offset. Thismethod is particularly useful for larger diameter vias where the powerdensity would be too low to be efficient in a direct pixel via machiningapproach. Using the techniques involving gas ambient control and correctdelays the via quality of a scanned via is improved greatly. Also thesidewall morphology and composition can be accurately controlled in thismanner. Finally, using multiple steps in the depthwise direction, thescanned via taper can be controlled to form a nozzle. A schematic ofthis approach is illustrated in FIG. 9. This is not limited to purelycircular vias. Elliptical via profiles are also possible through ascanning beam machining process.

[0211] Formation of Angled Vias

[0212] Aside from straight through vias and blind vias a furtherembodiment of the invention is the formation of angled vias. Thebenefits of angled vias include moving topside wafer bump connections tothe backside of the wafer, reducing topside area required forconnectivity and the ability to connect from topside or bottom-side to apoint at the edge of a micromachined side wall structure to enablecontact with an embedded device.

[0213] The logical approach to laser drilling micro-vias at an angle isto tilt the substrate with respect to the optic axis. In practice thisis not easy to implement as it will be difficult to maintain a constantworking distance between the lens and the work surface. Only along theaxis of tilt can this distance be maintained, with either side eithernearer or further from focus. While oscillating the tilt will have theeffect of widening the via without giving it any preferred angle inspace.

[0214] Over a 6″ wafer a tilt of as little as 10° will introduce avertical displacement of 26 mm at the periphery and even over a 10 mmsquare area the vertical displacement will be 1.74 mm which issignificantly outside the depth of focus of all but the longest scanninglenses.

[0215] To be used in such an instance would require automatic refocusingof the beam over the field of view to compensate for the differentrelative displacements of the work surface from the scan lens. This alsocan be achieved by moving the vertical position of the wafer dependingon the distance of the machining site from the axis of tilt.

[0216] In one embodiment of this invention a non-telecentric lens isused to form angled microvias. Such a lens is depicted in FIG. 10. Thelens diameter is D and the diagonal of the Field of View is L. Since thelens is non-telecentric the emergent beam is not orthogonal to the opticaxis (except when incident along the optic axis) and the largestavailable deviation angle is T, which is arctan((L−D)/2*WD). For atypical non-telecentric F-theta lens with a Working Distance of 188 mm,a lens diameter of 90 mm and a Field of View diagonal of 140 mm themaximum deviation angle is 7.6°.

[0217] The available range for angled vias is then, for this particularlens, between 0 and 7.6°. By employing appropriate lenses other rangesmay be achieved between 1 and 14°.

[0218] The range of angles available is determined by the scan angle ofthe galvanometer and the lens specification. To achieve control of anglerequires that the wafer position can be controlled relative to theobject field point at which the beam forms that angle relative to thenormal angle of the optical system. This can be achieved by an X-Y tablepositioning system synchronised with galvanometer and laser.

[0219] Variable Focus During Via Drilling

[0220] Zoom Telescope

[0221] Due to the finite depth of focus of the F-theta lens the viadiameter may change with propagation depth through the substrate,something which may be undesirable. To mitigate this a variable focussystem may be employed that will have the effect of modifying thefocused spot position during the drilling process. Such a systemutilises a zoom telescope in conjunction with the scan lens. Thetelescope permits the spot size at focus to be adjusted automaticallybetween 5 and 50 ∉n. An example of the optical configuration is shown inthe schematic of FIG. 11.

[0222] The telescope and scan lens system are constructed such that thecollimation of the beam upon exiting the telescope is tailored to permitthe scan lens come to a focus at any position within 5 mm of its nominalworking distance. This is illustrated in the graphic of FIG. 12.Automation and software control integrated into the machiningenvironment makes this method a highly reliable and sophisticatedsolution to the problem of maintaining precise control of via aspectratios. It is significantly easier than drilling some way into the vias,stopping, changing the focus manually by adjusting the galvanometer/scanlens position and then completing the via.

[0223] In one embodiment of the invention the available via diametersmay be configured to be between 5 and 200 ∉m by adjusting the zoomtelescope to an appropriate setting permitting a wide range of sizes tobe achieved.

[0224] In a further embodiment the speed of drilling can be increased byadjusting the collimation of the zoom telescope to bring about differentfocus positions within the workpiece, ensuring a consistent spot sizethrough the body of the via.

[0225] In a multi-step process the diameter of the via may be adjustedat each processing step permitting a precisely controlled via profile.

[0226] In a further embodiment the incident beam may, by defocusing thetelescope, be enlarged to a degree such that the incident intensity isless than the ablation threshold for the workpiece but higher than thecleaning threshold permitting explosive cleaning of the surface in thevicinity of the via entrance. This is depicted in FIG. 13.

[0227] In another version of the invention the sidewall of each via canbe cleaned as a final processing step by directing a beam of lower powerinto the via and traversing the sidewalls, thereby removing debris andimproving the quality of the finished surface.

[0228] Through appropriate adjustment of the main laser parameters suchas the pulsewidth, pulse energy and repetition rate, beam size anddivergence the taper angle of the via may be controlled.

[0229] Another embodiment of this invention is to control the wafervertical position relative to the beam waist at each step in themulti-step process. Variation of the vertical position relative to thewaist has the effect of modifying the beam size at each step. This isanalogous to controlling the plane of focus for a fixed beam diameter.

[0230] The following summarises features of the invention.

[0231] Producing high quality microvia structures in semiconductor andinsulator materials by means of a multi-step laser machining process.

[0232] Producing high quality microvia structures in semiconductor andinsulator materials by means of a controlled gaseous environmentpermitting control of the internal wall morphology and materialcomposition of the microvia structure.

[0233] Producing high quality microvia structures in semiconductor andinsulator materials by means of both a controlled gaseous environmentand a multi-step laser machining process.

[0234] The laser pulse energy, laser pulse separation and the number oflaser pulses per machining step are selected based on the substrateoptical, thermal and mechanical properties, the laser type and the depthwithin the substrate.

[0235] A controlled amount of oxygen or an oxygen-containing gas is usedin a gas reaction chamber during laser machining in order to promotecontrolled oxide growth on the internal walls of the microvia structure.

[0236] A controlled amount of an inert gas is used in a gas reactionchamber during laser machining in order to suppress the growth of anoxide layer on the internal walls of the microvia structure.

[0237] A gas, upon photo- or thermal-dissociation in the presence of themachining laser beam, produces by-products that are etchants of thesubstrate to be machined, thus permitting cleaner machining of themicrovia structure and reduction of debris at the microvia entrance andexit and on the internal walls.

[0238] A gas, which is naturally reactive with by-products of the laserinduced material removal preventing deposition of reacted species.

[0239] A multi-step laser machining process is used to control thethermal loading in the substrate material thus preventing thermal shockleading to cracking and damage to the internal microvia walls.

[0240] A microvia structure with a diameter in excess of 100 microns ismachined by scanning of the laser beam in a pattern comprising of aseries of concentric circles.

[0241] A microvia structure with a diameter less than 100 microns ismachined using a laser beam held in a fixed position on the substratesurface.

[0242] The focal spot size of the laser beam is altered using anautomated beam telescope during machining of the microvia structure inorder to define the internal side-wall contour.

[0243] Subsequent to machining of the microvia structure the focal spotsize of the laser beam is increased so as to permit laser cleaning ofthe debris field on the surface of the substrate surrounding themicrovia entrance aperture.

[0244] The laser focal spot is scanned through the substrate materialduring machining of the microvia structure by adjusting the collimationof an automated beam telescope resulting in control of the internalside-wall contour of the microvia structure.

[0245] A sloped microvia structure is drilled at an acute angle bytilting the wafer with respect to the beam.

[0246] In one embodiment, the microvia is drilled at an acute angle withrespect to a substrate surface using a non-telecentric lens thuspermitting access to a device within the substrate, thereby allowing alayered component architecture and also allowing tighter geometricpositioning of components.

[0247] A series of sloped microvia structures are machined from a commonentrance aperture on one side of a substrate to the same or differentdepths in the interior or to the bottom of the substrate, thuspermitting electrical connection of multiple points in the substratewith a common point on the substrate surface following insertion ofconducting material into the microvia structures.

[0248] A series of sloped microvia structures are machined from one sideof a substrate to connect with a common point in the interior or on theother side of the substrate, thus permitting electrical connection ofmultiple points in the substrate surface with a common point on thesubstrate interior or on the other site of the substrate followinginsertion of conducting material into the microvia structures.

[0249] A via is drilled through the substrate to electricallyinterconnect opposed sides of the substrate.

[0250] A via is drilled as a blind via or through via to facilitatethermal contacting and heat dissipation.

[0251] The substrate is of silicon material and the insulating lining isof SiO₂.

[0252] The laser beam has a wavelength in the VIS-UV range.

[0253] Example of Application of the Invention

[0254] In recent years there have been major developments in productionof integrated electronic components. However, because of the mechanicalrequirements for positioning of items such as waveguides and opticalsources and detectors automation of production of optical components hasnot been achieved to any significant extent.

[0255] This invention enables device structures that simplifymanufacturability of such components.

[0256] For example an optical component may be produced by:

[0257] providing a substrate;

[0258] etching a trench in the substrate using a laser beam; and

[0259] mounting an optical device in the trench.

[0260] The method comprises the further steps of laser drilling vias toprovide electrical conductors. Additionally, the capability to machine asloped via drilled at an angle with respect to a substrate surface foraccess to a device within the substrate allows a layered componentarchitecture. The benefit of such a structure is that multiple contactpads on one side of the wafer or substrate can be connected to a singlepad or trench on the opposing side of the wafer or substrate. Asdescribed previously the system allows formation of an Si/SiO2 oralternative insulating lining on the via.

[0261] Referring to FIGS. 14 and 15, a substrate 101 for an opticalcomponent is illustrated. The substrate is a Silicon Optical Bench(SiOB). The substrate 101 comprises a V-shaped groove 102 and trenches103 and 104 for an optical source and associated Peltier thermal controlelements. Sloped microvias 105 are laser drilled to reach the trenchesfor electrical connection. Laser drilling is also used to createmounting holes 106. Also, through vias (not shown) are drilled throughthe substrate for electrical access of one side to the other.

[0262] In the drawings, an optical fibre is indicated by the numeral 10,in which there is a core 111 and cladding 112. The etching progress isillustrated in FIG. 17, in which a spot pattern 116 is illustrated.

[0263] The use of angled (sloped) vias allows layering of layeredcomponents in which components are placed one above the other, whilestill making required electrical contacts. This allows increasedcomponent density. One architecture is placing of electrical circuits onthe substrate surface and optical devices within the substrate body.

[0264] An aspect of the laser via drilling is that by appropriatecontrol of the drilling parameters and gases such as oxygen aninsulating lining is inherently created. Thus the solder which is filledinto the vias is insulated from the surrounding semiconductor materialwithout the need for adding a discrete insulating lining. Thickness ofthe insulating lining can be controlled by suitable control of the laserparameters and gas environment. In one embodiment, the laser beams areUV or visible, for example 355 nm/266 nm UV systems and 532 nm Greenlaser systems and having a repetition frequency greater than 1 kHz.

[0265] Referring to FIGS. 20 to 22, the methods by which the sloped viasare drilled is illustrated. As shown in FIGS. 20 and 21, anon-telecentric lens is used to direct the output from a galvanometerlaser head.

[0266] Referring to FIG. 22, an alternative method is to tilt at anappropriate angle using a tilt stage. It may be necessary to adjust theheight of the wafer to ensure the depth of focus is correct. However ifthe wafer can be tilted about the particular point where the via is tobe formed this adjustment of height may not be necessary. i.e. therequired change in depth is simply the distance of the via from the tiltpoint times the sine of 90θminus the required angle for the via.

[0267] Referring again to FIGS. 14 to 19, there are angled vias whoseentrances are on the top of the wafer and which exit in the chamberwhere the laser will be placed. The laser is on its side allowing forthe electrical connects. A chamber beneath the laser is created for athermistor and the whole system is placed on a peltier. The laser isplaced in the chamber and then appropriate electrical material is placedin the trench ensuring that safe clean contacts are made with the laserwithout causing damage to it. The ‘ground’ trench could be placed to theright of the chamber with the appropriate electrical material helping tokeep the laser chip stable.

[0268] The laser sources for drilling and etching are second and higherorder harmonic frequency solid state lasers operating with high pulseenergies and nanosecond pulse widths. Implementation of the invention ispossible with shorter pulse width lasers but central to the highthroughput aspect of this invention is that the laser must operate at ahigh repetition rate.

[0269] The following are advantageous features of the invention.

[0270] The formation of V-grooves on an integrated optical chip (IOC)used for optical fibre alignment by laser ablation, using, for examplean Nd:Yag frequency tripled or quadrupled laser. Where SiOB is theobjective, 355 nm and 266 nm are particularly useful. Where LiNbO3 andinsulating substrates are used 266 nm (or fourth harmonic) lasers arethe preferred option.

[0271] The formation, by laser ablation, of component slots or trenchesfor alignment and/or housing of, for example laser diode chips orphotodiode chips represent examples of blind vias.

[0272] The formation, by laser ablation of through-vias on an integratedoptical chip (IOC) to allow electrical contacts from one side through tothe other side of a wafer.

[0273] The formation, by laser ablation, of sloped or angledthrough-vias where typically the vias start at the top (or bottom orside) of the wafer and will exit in a trench allowing for preciseelectrical connections to a particular component to be placed in thetrench. In the case of silicon, with a specific set of laser parameters,the via side wall composition may be controlled to consist of glass likesilicon dioxide. The composition and structure of this oxide may furtherbe controlled by the presence or absence of a gas and the laserparameters. For example removal of oxygen from the ablation reactionwill reduce the amount of SiO2.

[0274] In another embodiment, the microvia enables formation of anoptical waveguide through connection. The waveguide structure is definedby a cladding and a core region. In this example the cladding is formedpartially by control of the laser machining parameters and gasenvironment so that a glassy layer is formed on the internal viaside-wall. The optical waveguide can then be formed through filling thevia with appropriate plastic or glass material with sufficiently hightransmission to form an optical waveguide through via.

[0275] Example of Application of the Invention

[0276] Angled vias can be of use for shrinking the size of a die,especially in the case of die which have active devices and pads on thesame side and which have comparable areas of the die utilized by thepads and the devices. This is of particular interest for these caseswhere the devices have a low number of I/O connections, but can stillhold true for die with a larger number of I/O connections where theedges of the die contain the majority of the pads (edge-leaded die).

[0277] In one embodiment of the invention, the device would exist on oneside of the die with its position roughly centered on the die face (seeFIG. 23). The I/Os are distributed around this device. Vias are drilledfrom the contact locations on the device to a series of pads. Instead ofusing pads which extend outward from the device to the edge of the dieas in FIG. 23A, the vias are metallized (or otherwise made intoconduction paths), and pads are now formed on the back of the die as inFIG. 23B. The angle of the vias allows for the I/Os to be positioned allthe way in to the center of the die backside, allowing for uniformpopulation of the surface of the back of the die.

[0278] Now that the device is the only feature on the front side of thewafer, the die size may be significantly reduced (by the area which waspreviously taken up by the bond pads). This not only allows for smallerdie and smaller package sizes, but also allows more die to be created onthe same wafer during wafer fabrication. While the first of thesebenefits is primarily a product feature benefit (smaller die, less realestate wasted in the final device), the latter one has the potential tosignificantly reduce the manufacturing costs incurred in waferfabrication for making these devices (the same number of die can be madeon fewer wafers).

[0279] In a further embodiment of the invention that is specific to thisexample the vias don't necessarily have to be angled, particularly whenthere is a small number of I/O connections from the active device. Inthis instance, straight vias can be machined from the contact locationson the device through to pads located on the backside of the die. Viasat the edge of the die will connect to pads on the bottom side of thedie that can be patterned in towards the centre of the die, thusmaintaining the footprint of the active device from the top to thebottom of the die and thereby still permitting an increased number ofactive devices on the front side of the wafer.

[0280] In a further embodiment of the invention, angled vias can beuseful for redistribution of I/O connections on a die. In a typicalbumped die, approximately a third of the I/O connections are for eitherpower or ground. When these leads go out to the package, all the groundsare connected together and all the power leads are also connected. Onlythe signal leads need to remain independent. As such, angled vias allowfor an altogether new approach. The grounds and/or the power leads canbe connected at the pads themselves when the wafer is bumped on theback. In this technique, angled vias would point in different directionsfrom the bump with respect to the in-plane component of their trajectory(see FIG. 24). As such, one bump on the back of the wafer can beconnected to multiple contact points on the front of the wafer (e.g. onepad for four ground contacts is feasible).

[0281] The invention is not limited to the embodiments described but maybe varied in construction and detail.

1. A laser machining system comprising a laser source, and a beamdelivery system comprising means for controlling delivery of a laserbeam generated by the laser source to a substrate to machine thesubstrate, wherein the system further comprises a gas handling systemcomprising means for providing a controlled gaseous environment around amachining site.
 2. A system as claimed in claim 1, wherein the beamdelivery system and the gas handling system comprise means forcontrolling beam pulsing parameters and the gaseous environment to drilla via in the substrate.
 3. A system as claimed in claim 1, wherein thebeam delivery system comprises means for controlling laser pulse energy,laser pulse separation, and number of pulses according to the optical,thermal, and mechanical properties of the material(s) being machined. 4.A system as claimed in claim 1, wherein the gas handling systemcomprises means for controlling proportion of oxygen in the gaseousenvironment to control or prevent or promote oxide growth as a lining.5. A system as claimed in claim 1, wherein the gas handling systemcomprises means for controlling proportion of nitrogen in the gaseousenvironment to control or prevent nitride growth in a lining.
 6. Asystem as claimed in claim 1, wherein the gas handling system comprisesmeans for providing a controlled amount of inert gas in the gaseousenvironment.
 7. A system as claimed in claim 1, wherein the gas handlingsystem comprises means for introducing into the gaseous environment agas which has properties for dissociation in the presence of the laserbeam to provide etchants or reactants of the substrate.
 8. A system asclaimed in claim 1, wherein the gas handling system comprises means forcontrolling the gaseous environment to achieve a clean machined wall inthe substrate.
 9. A system as claimed in any claim 1, wherein the gashandling system comprises means for controlling the gaseous environmentto achieve a desired smoothness in a machined wall of the substrate. 10.A system as claimed in claim, 1 wherein the gas handling systemcomprises means for controlling the gaseous environment to enhanceremoval of debris from the machining site and locality or to reduce thequantity of debris that is generated.
 11. A system as claimed in claim1, wherein the beam delivery system comprises means for controllingpulsing parameters to minimise thermal damage to the substrate.
 12. Asystem as claimed in claim 11 wherein the laser pulses are not evenlyspaced in time.
 13. A system as claimed in claim 1, wherein the beamdelivery system comprises a non-telecentric lens, and means fordelivering the laser beam through said lens at an angle to normal todrill a sloped via.
 14. A system as claimed in claim 13, wherein thebeam delivery system comprises means for varying distance of a slopedvia entry opening from a beam optical axis to set slope of the slopedvia.
 15. A system as claimed claim 1 wherein the beam delivery systemcomprises means for drilling a via in the substrate and for dynamicallyvarying laser beam parameters as a function of current via depth.
 16. Asystem as claimed in claim 15, wherein the beam delivery systemcomprises means for varying laser beam parameters according to materialof the substrate at any particular depth.
 17. A system as claimed inclaim 15, wherein the beam delivery system comprises means for varyinglaser beam parameters with depth in order to achieve a desired viageometry.
 18. A system as claimed in claim 17, wherein said varyingmeans comprises means for varying the laser beam parameters to drill ablind via.
 19. A system as claimed in claim 15, wherein the beamdelivery system comprises means for varying laser beam parameters withdepth in order to achieve a controlled via diameter at the entrance andexit points on the substrate.
 20. A system as claimed in claim 19,wherein the varying means comprises means for controlling slope of ataper between the entry and exit openings by varying laser repetitionrate, pulse energy, and pulse peak power.
 21. A system as claimed inclaim 20, wherein the varying means comprises means for varying focalspot size to control internal via shape.
 22. A system as claimed inclaim 1, wherein the beam delivery system comprises a telescope, andmeans for adjusting the telescope to set or dynamically vary beamdiameter, plane of focus, and depth of focus to provide a desired viageometry.
 23. A system as claimed in claim 1, wherein the beam deliverysystem comprises means for machining the substrate in a plurality ofpasses, in which each pass machines to a certain stage with a proportionof material removal.
 24. A system as claimed in claim 23 when dependenton claim 22, wherein the beam delivery system comprises means foradjusting the telescope between passes.
 25. A system as claimed in claim1, wherein the beam delivery system comprises means for enlarging laserbeam focal spot size after drilling a via to cause laser cleaning ofdebris on the surface of the substrate surrounding the via.
 26. A systemas claimed in claim 1, wherein the gas handling system and the beamdelivery system comprise means for controlling laser pulsing and thegaseous environment to provide a controlled insulating lining in a viadrilled in a semiconductor substrate.
 27. A system as claimed in claim26, wherein the substrate is of Si material and the lining is SiO₂. 28.A system as claimed claim 1, wherein the gas handling system comprises asealed chamber, means for delivery of gases into the chamber and meansfor pumping gases from the chamber.
 29. A system as claimed in claim 28,wherein the chamber comprises a window which is transparent to the laserbeam.
 30. A system as claimed in claim 1, wherein the gas handlingsystem comprises means for delivering a halogenated gas to the gaseousenvironment to remove gaseous debris.
 31. A system as claimed in claim,1 wherein the gas handling system comprises means for controlling gasflow for removal of debris in both gaseous and particulate form.
 32. Asystem as claimed in a claim 1, wherein the system further comprisesmeans for flipping a substrate, and the beam delivery system comprisesmeans for drilling at locations in registry at opposed substratesurfaces to complete a through via.
 33. A system as claimed in claim 1,wherein the beam delivery system and the gas handling system comprisemeans for controlling beam pulsing parameters and the gaseousenvironment to drill a via having a lining suitable for use as anelectrical insulator.
 34. A system as claimed in claim 1, wherein thebeam delivery system and the gas handling system comprise means forcontrolling beam pulsing parameters and the gaseous environment to drilla via having a lining suitable for use as an optical waveguide cladding.35. A method in which the systems of claim 1 is used to machine asubstrate or workpiece.
 36. A laser machining method comprising thesteps of delivering a laser beam onto a substrate to machine thesubstrate, wherein a gaseous environment is provided around a machiningsite; the laser beam is pulsed; and the laser beam and the gaseousenvironment are controlled to machine the substrate to achieve desiredproperties in the substrate.
 37. A method as claimed in claim 36,wherein laser pulse energy, laser pulse separation, and number of pulsesare controlled according to substrate optical, thermal, and mechanicalproperties.
 38. A method as claimed in claim 36, wherein oxygen ornitrogen concentration in the gaseous environment is controlled tocontrol or prevent oxide or nitride growth as a via lining.
 39. A methodas claimed in claim 38, wherein a controlled amount of inert gas isintroduced into the gaseous environment. 40 A method as claimed claim36, wherein a gas having properties for dissociation in the presence ofthe laser beam is introduced into the gaseous environment, and thedissociated gases etch the substrate.
 41. A method as claimed in claim36, wherein the machining is to drill a via and laser beam parametersare dynamically varied as a function of current via depth.
 42. A methodas claimed in claim 36, wherein the laser beam and the gaseousenvironment are controlled to provide an electrically insulating lining,and the method comprises the further step of filling the via with anelectrically conducting material to provide an electrical conductor inthe substrate.
 43. A method as claimed in claim 36, wherein the laserbeam and the gaseous environment are controlled to provide an opticallyopaque lining, and the method comprises the further step of filling thevia with an optically transmissive material to provide an opticalwaveguide in the substrate with the lining as a cladding.
 44. A methodas claimed in claim 36, wherein the laser beam and the gaseousenvironment are controlled to provide a thermally conductive path, andthe method comprises the further step of filling the via with athermally conductive material to provide a thermally conductive path inthe substrate.
 45. A method as claimed in claim 44 comprising thefurther step of connecting a heat sink to the thermally conductivematerial in the via.
 46. A laser machining system comprising a lasersource, and a beam delivery system comprising means for controllingdelivery of a laser beam generated by the laser source to a substrate tomachine the substrate, wherein the beam delivery system comprises meansfor delivering a pulsed laser beam to a substrate; and the beam deliverysystem comprises means for machining the substrate to an incompletestage at a plurality of machining sites, and for machining at said sitesin at least one subsequent pass whereby there is a delay betweenmachining at any one site as the other sites are machined in a pass. 47.A system as claimed in claim 46, wherein the beam delivery systemcomprises means for changing beam delivery parameters between passes.48. A system as claimed in claim 47, wherein the beam delivery systemcomprises means for changing beam delivery parameters between passesaccording to the substrate layer material for a pass.
 49. A system asclaimed in claim 47, wherein the beam delivery system comprises meansfor changing beam delivery parameters between passes according todesired substrate shape at the machining sites.
 50. A system as claimedin claim 46, wherein the beam delivery system comprises means forcontrolling beam delivery parameters between passes to minimisesubstrate thermal damage.
 51. A system as claimed in claim 46, whereinthe beam delivery system comprises means for controlling beam deliveryparameters between passes to reduce deposition of debris.
 52. A systemas claimed in claim 46, wherein the beam delivery system comprises meansfor controlling beam delivery parameters between passes to achieve adesired substrate geometry at the machining sites.
 53. A system asclaimed in claim 46, wherein the beam delivery system comprises meansfor controlling beam delivery parameters between passes to drill aplurality of vias in the substrate.
 54. A system as claimed in claim 46,wherein the system further comprises means for flipping a substrate andthe beam delivery system comprises means for machining the substrate atmachining sites on opposed sides of the substrate in registry to machinea single formation.
 55. A system as claimed in claim 46, wherein thebeam delivery system comprises means for controlling beam deliveryparameters to both machine the substrate and to form an electricallyinsulating lining at the machined site.
 56. A system as claimed in claim46 wherein the system also has a gas handling system in which the gasand gas parameters may be changed between subsequent passes.
 57. Asystem as claimed in claim 55, wherein the system further comprises agas handling system comprising means for providing a controlled gaseousenvironment around the machining site, and the beam delivery system andthe gas handling system comprise means for machining a formation in thesubstrate with or without non-ambient gas in one pass, and for machiningat the site in a subsequent pass with a non-ambient gaseous environmentto form an insulating lining at the machining site.
 58. A lasermachining method comprising the steps of delivering a laser beam onto asubstrate to machine the substrate, wherein the beam is delivered tomachine the substrate at a plurality of sites in a pass, and tosubsequently drill at the same sites in at least one subsequent pass tocomplete machining at each site.
 59. A method as claimed in claim 58wherein a via is drilled at each site.
 60. A method as claimed in claim58, wherein beam delivery is controlled to both machine a formation ateach site and to provide an electrically insulating lining on asubstrate wall at each site.
 61. A method as claimed in claim 60,wherein a controlled gaseous environment is provided at the machiningsites to assist lining growth in a controlled manner.
 62. A method inwhich the system of claim 56 is used in a manner in which the gas andgas parameters may be changed between subsequent passes.
 63. A lasermachining system comprising a laser source, and a beam delivery systemcomprising means for controlling delivery of a laser beam generated bythe laser source to a substrate to machine the substrate, wherein thebeam delivery system comprises means for delivering a pulsed laser beamto a substrate at an angle to drill a sloped via.
 64. A laser machiningmethod comprising the steps of delivering a laser beam onto a substrateto machine the substrate, wherein the laser beam is pulsed, and the beamis delivered at an angle to drill a sloped via.
 65. A method as claimedin claim 64, wherein the via is drilled to interconnect layers in thesubstrate.
 66. A method as claimed in claim 64, wherein the via isdrilled for conformity with component leads to be mounted on thesubstrate.
 67. A method as claimed in claim 64, wherein a plurality ofinterconnecting vias are drilled
 68. A method as claimed in claim 67,wherein the vias are drilled to interconnect at the substrate surface.69. A method as claimed in claim 68, wherein the vias are drilled tointerconnect internally within the substrate and to each have a separateopening in a substrate surface.
 70. A laser machining method comprisingthe steps of delivering a laser beam onto a substrate to machine thesubstrate, wherein the laser beam is pulsed and is delivered to drill avia in the substrate, and the method comprises the further step offilling the via with a thermally conductive material to provide athermal conductor.
 71. A method as claimed in claim 70, comprising thefurther steps of connecting a heat sink to the thermally conductivematerial.
 72. A method as claimed in claim 71 comprising the furtherstep of drilling another via adjacent to said via and filling said othervia with an electrically conductive material, and connecting anelectrical component to said electrically conductive material.
 73. Amethod as claimed in claim 70, wherein the via is a blind via.
 74. Amethod as claimed in claim 70 in which the angled vias are generated ina geometry that allows multiple via contact points on one side of asubstrate to a single contact point on the other side of the substrate.75. A method as claimed in claim 74 in which multiple power inputs andoutputs or multiple ground inputs and outputs are consolidated to areduced number inputs and outputs.
 76. A method in claim 70 in whichangled vias are used to reduce the size of a device by allowingconnection pads to be placed on the back side of the die.
 77. A systemas claimed in claim 1, 46 or 63 wherein the laser source is a solidstate diode pumped laser source.
 78. A method as claimed in claim 36,58, 64, or 70 wherein the laser beam is generated by a solid state diodepumped laser source
 79. A system as claimed in claim 77 where the lasersource is a frequency multiplied solid state laser source.
 80. A methodas claimed in claim 78, where the laser source is a frequency multipliedsolid state laser source.
 81. A system as claimed in claim 77 where thelaser is a solid state laser where the laser medium is of the typeHost:Impurity where the host is YAG, YLF, Vanadate.
 82. A method asclaimed in claim 78, where the laser source is a solid state lasersource in which the laser medium is of the type Host:Impurity and inwhich the host is YAG, YLF, Vanadate.
 83. A system as claimed in claim77 wherein the laser repetition frequency is in the range from 1 kHz to200 kHz
 84. A method as claimed in claim 78, wherein the laserrepetition frequency is in the range from 1 kHz to 200 kHz
 85. A systemas claimed in claim 77 where the laser source comprises means forgenerating a laser beam with pulsewidth less than 200 nanoseconds.
 86. Amethod as claimed in claim 78, wherein the laser pulsewidth is less than200 nanoseconds.
 87. A system as claimed in claim 77 wherein the lasersource comprises means for generating a laser beam with a pulsewidthless than 10 nanoseconds.
 88. A method as claimed in claim 78, whereinthe laser pulsewidth is less than 10 nanoseconds